1. Field of the Invention
The present invention relates to a flat fluorescent lamp having improvements in mating the same with a lamp holder. Further, the present invention relates to a liquid crystal display (LCD) device into which such a flat fluorescent lamp is incorporated.
2. Description of Related Art
Liquid crystal materials emit no light of their own, so that LCDs require a separate source of luminance. Fluorescent tubes are commonly used as the illumination sources in LCD backlights because they have the requisite properties of high efficiency, long life, etc. Small diameter straight fluorescent tubes are usually used as edge-light illuminators. On the other hand, single or multiple or serpentine fluorescent tubes are used as the direct backlight illuminators. However, in order to evenly illuminate the entire surface thereof, the direct backlight illuminators should sufficiently be held away from the LCDs, and accordingly, they become undesirably bulky. Further, such direct backlight illuminators itself is also bulky due to the usage of fluorescent tubes. In an effort to preclude this problem, flat or planar fluorescent lamps have proposed and they are gaining in popularity because of their high luminance and small depth sizes.
Prior to turning to the present invention, it is deemed preferable to briefly describe a conventional flat fluorescent lamp with reference to FIGS. 1-3,
FIG. 1 is a partially taken away perspective view of a conventional fluorescent lamp (denoted by 10). As shown, two glass plates 12 and 14 are hermetically bonded to opposite sides of a rectangular frame 16 so as to form a discharge chamber 18. The glass plates 12 and 14 are aligned with respect to the edges or peripheries thereof when bonded to the frame 16. The peripheries of the glass plates 12 and 14 extend beyond the frame 16. By way of example, each of the glass plates 12 and 14 has a thickness of about 2 mm, and the rail of the frame 16 is about 4 mm both in thickness (height) and in width.
FIG. 2 is a cross-section of part of the flat fluorescent lamp of FIG. 1. As shown in FIG. 2, the glass plate 12 carries, on the inner surface thereof, a phosphor coating 20 that extends to in the vicinity of the upper inner corner of the chamber 18. On the other hand, the glass plate 14 is provided with, on the inner surface thereof, a plurality of pairs of plus (+) and minus (xe2x88x92) electrodes (only one pair 22a-22b is shown), which are covered by dielectric film (layer) 24 which is in turn covered by a light reflective film or coating (not shown). The glass plates 12 and 14 are hermitically bonded to the frame 16 using substrate frits 26 (for example). In order to secure a predetermined gap or distance, which equal to the height of the frame 10, between the glass plates 12 and 14, a plurality of spherical spacers 28 (only one is shown) are provided within the chamber 18.
It is necessary to select the materials of the glasses 12, 14, frame 16, and frits 26 so that the coefficients of linear expansion thereof are substantially identical. This is important to prevent the parts from being undesirably deformed or damaged due to thermal stress. Each of the glass plates 12 and 14 is typically made of soda-lime glass, and the frame may be made of the same material, borosilicate glass, or ceramics such as aluminium oxide or calcium oxide. As is well known, the chamber 18 is filled with an inert gas (rare gas) or an inert gas plus mercury vapor. When electric energy is applied to the lamp 10, an electric plasma arc is formed between the electrodes 22a and 22b through the mercury vapor to produce ultraviolet light rays which bombers the phosphor coating 20, causing the coating 20 to emit light in visible spectrum.
FIG. 3 is a schematic sectional view of part of a LCD device 40 wherein the flat fluorescent lamp 10 of FIG. 1 is incorporated. A parts holder or supporter 42 is provided at the corner of a rear frame 44, which holder 42 holds the parts including the flat fluorescent lamp 10 thereby determining the positions thereof. This rear frame 44 is typically made of appropriate metal and is shaped as shown, which Is applicable to other frames: intermediate frame 46 and front frame 48.
The flat fluorescent lamp 10 is placed on the bottom of the rear frame 44 such that the glass plates 12 and 14 abut onto the sidewall of the parts holder 42 at the ends thereof, and accordingly the lamp 10 is set in the prescribed position. Deposited on the flat fluorescent lamp 10 is a light diffusion plate 50 that is also set to the preset position by the holder 42. The light diffusion plate 50 is to diffuse the light emitted from the lamp 10, via which a LCD panel 52 can evenly be illuminated.
As shown in FIG. 3, the holder 42 also sets the light diffusion plate 50 in the preset position. As is well known, the LCD panel 52 comprises two transparent substrates spaced apart by a seal having a thickness of about 10 xcexcm (for example). In the case illustrated, only the lower substrate (denoted by 53) extends such as to abut onto the projection 64 extending integrally from the holder 42. The extended portion of the substrate 53 carries thereon a plurality of bonding pads, electrical lines, etc.
As mentioned above, the lamp 10 is set in the predetermined position by abutting the edges of the two glass plates 12 and 14 onto the parts holder 42. In order to precisely position the lamp 10 within the LCD device 40, it is necessary to exactly align the edges of the two glass plates 12 and 14 in a direction normal to the main surfaces of the glass plates 12 and 14. In the case where a misalignment occurs with the edges of the glass plates 12 and 14, it is no longer expected to precisely abut both the edges of the two glass plates 12 and 14 onto the sidewall of the holder 42. The causes of potential misalignment reside in both manufacturing the glass plates and bonding them to the frame 16. Further, since the tolerances are admitted at both manufacturing and bonding of the glass plates, it is in fact extremely difficult to precisely align the glass plates. Accordingly, the conventional flat fluorescent lamp 10 suffers from the problems that the lamp 10 is typically unable to be held firmly by the holder 16 and incur play at the abutting area, which leads to the lowering of the shook resistance of the lamp 10 and reliability of the LCD device as the whole.
It is therefore an object of the present Invention to provide a flat fluorescent lamp which features improvements in coupling the same to a lamp holder, thereby to overcome the aforesaid problems inherent in the conventional flat fluorescent lamp.
Another object of the present invention is to provide a LCD device which incorporates therein a flat fluorescent lamp featuring improvements in coupling the same to a lamp holder, thereby increasing the reliability of the device in terms of shook or impact resistance and so on.
In brief, these objects are achieved by the techniques wherein a flat fluorescent lamp is provided with one or more protrusions at the periphery thereof, which protrusion(s) extends outwardly beyond the edges of the two glass plates. A lamp holder receives the protrusion of the flat fluorescent lamp so as to hold the same in a manner that no edges of the two parallel glass plates touch or come into contact with the lamp holder.
One aspect of the present invention resides in a flat fluorescent lamp comprising: a sealed chamber formed by a chamber frame and first and second glass plates, which glass plates are bonded to opposite sides of the chamber frame in alignment with the edges thereof; a phosphor coating provided on an inner surface of the first glass plate; and a plurality of electrodes provided on an inner surface of the second glass plate for inducing electric discharge within the chamber; wherein the chamber frame is provided with mating means via which the flat fluorescent lamp is held within a lamp holding frame, the mating means protruding from the chamber frame in parallel with the two glass plates beyond the edges of the two glass plates such as to leave space between the edges of the glass plates and the lamp holding frame.
Another aspect of the present invention resides in a liquid crystal display device, comprising: a liquid crystal display panel; a flat fluorescent lamp for emitting light therefrom, the flat fluorescent lamp positioned so as to illuminate the liquid crystal display panel from behind, the flat fluorescent lamp comprising a sealed chamber formed by a chamber frame and first and second glass plates, which glass plates are bonded to opposite sides of the chamber frame in alignment with the edges thereof; and a light diffusion plate provided between the flat fluorescent lamp and the liquid crystal display panel, wherein the chamber frame is provided with mating means via which the flat fluorescent lamp is held within a lamp holding frame, the mating means protruding from the chamber frame in parallel with the two glass plates beyond the edges of the two glass plates such as to leave space between the edges of the glass plates and the lamp holding frame.